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Pick the part to render from multipart/alternative: related start brackets · case 01

A multipart/related alternative whose start parameter names a later root is judged by its first child (an image) and skipped.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The related start brackets decision evaluates `c.get('cid') == start` where the contract requires `c.get('cid') == start.strip('<>')`.

VERIFIED REPAIR

Use `c.get('cid') == start.strip('<>')` for the related start brackets decision and keep every other rule of the model unchanged.

Unsuccessful approach: Removing only the opening bracket still leaves the closing bracket on the start reference. The attempted `c.get('cid') == start[1:]` still disagrees with a fixture.

Case contract

Alternatives are ordered by increasing fidelity, so the LAST part whose effective type is in `supported` wins. A multipart/related alternative counts as its root type: the child whose cid equals the start parameter (which carries angle brackets, cids are stored bare) or else the first child. A text/* part is only renderable when its charset (default us-ascii, case-insensitive) is us-ascii, utf-8 or iso-8859-1. With nothing renderable the first part is shown as a fallback. Result {index, type, fallback}.

Why this case matters

Choosing the wrong alternative shows raw markup, a degraded body or an unreadable charset to the reader.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(part, supported):
    def effective(p):
        if p['type'] == 'multipart/related':
            start = p.get('params', {}).get('start')
            for c in p['parts']:
                if start is not None and c.get('cid') == start:
                    return c['type']
            return p['parts'][0]['type'] if p['parts'] else None
        return p['type']
    ok_charsets = ('us-ascii', 'utf-8', 'iso-8859-1')
    best = None
    for i, p in enumerate(part['parts']):
        t = effective(p)
        cs = p.get('params', {}).get('charset', 'us-ascii').lower()
        if t in supported and (not t.startswith('text/') or cs in ok_charsets):
            best = i
    if best is None:
        return {'index': 0, 'type': effective(part['parts'][0]), 'fallback': True}
    return {'index': best, 'type': effective(part['parts'][best]), 'fallback': False}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown1'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root1@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root1@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'ISO-8859-1'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 2: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown2'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root2@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root2@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'UTF-8'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 3: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown3'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root3@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root3@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'ISO-8859-1'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 4: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown4'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root4@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root4@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'UTF-8'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 5: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown5'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root5@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root5@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'ISO-8859-1'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
richest supported last{'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}{'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}Passed
unsupported last part{'fallback': False, 'index': 1, 'type': 'text/html'}{'fallback': False, 'index': 1, 'type': 'text/html'}Passed
related root via start{'fallback': False, 'index': 0, 'type': 'text/plain'}{'fallback': False, 'index': 1, 'type': 'text/html'}Failed
upper-case charset{'fallback': False, 'index': 1, 'type': 'text/html'}{'fallback': False, 'index': 1, 'type': 'text/html'}Passed
missing charset{'fallback': False, 'index': 1, 'type': 'text/html'}{'fallback': False, 'index': 1, 'type': 'text/html'}Passed
unknown charset html{'fallback': False, 'index': 0, 'type': 'text/plain'}{'fallback': False, 'index': 0, 'type': 'text/plain'}Passed
nothing supported{'fallback': True, 'index': 0, 'type': 'application/x-foo'}{'fallback': True, 'index': 0, 'type': 'application/x-foo'}Passed

SHA-256 / 0dba42c8c59f2cd98cf30cd9df6922577d9785059b4fa216ad959e61365c6d92

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(part, supported):
    def effective(p):
        if p['type'] == 'multipart/related':
            start = p.get('params', {}).get('start')
            for c in p['parts']:
                if start is not None and c.get('cid') == start[1:]:
                    return c['type']
            return p['parts'][0]['type'] if p['parts'] else None
        return p['type']
    ok_charsets = ('us-ascii', 'utf-8', 'iso-8859-1')
    best = None
    for i, p in enumerate(part['parts']):
        t = effective(p)
        cs = p.get('params', {}).get('charset', 'us-ascii').lower()
        if t in supported and (not t.startswith('text/') or cs in ok_charsets):
            best = i
    if best is None:
        return {'index': 0, 'type': effective(part['parts'][0]), 'fallback': True}
    return {'index': best, 'type': effective(part['parts'][best]), 'fallback': False}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown1'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root1@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root1@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'ISO-8859-1'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 2: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown2'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root2@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root2@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'UTF-8'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 3: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown3'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root3@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root3@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'ISO-8859-1'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 4: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown4'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root4@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root4@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'UTF-8'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 5: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown5'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root5@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root5@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'ISO-8859-1'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
richest supported last{'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}{'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}Passed
unsupported last part{'fallback': False, 'index': 1, 'type': 'text/html'}{'fallback': False, 'index': 1, 'type': 'text/html'}Passed
related root via start{'fallback': False, 'index': 0, 'type': 'text/plain'}{'fallback': False, 'index': 1, 'type': 'text/html'}Failed
upper-case charset{'fallback': False, 'index': 1, 'type': 'text/html'}{'fallback': False, 'index': 1, 'type': 'text/html'}Passed
missing charset{'fallback': False, 'index': 1, 'type': 'text/html'}{'fallback': False, 'index': 1, 'type': 'text/html'}Passed
unknown charset html{'fallback': False, 'index': 0, 'type': 'text/plain'}{'fallback': False, 'index': 0, 'type': 'text/plain'}Passed
nothing supported{'fallback': True, 'index': 0, 'type': 'application/x-foo'}{'fallback': True, 'index': 0, 'type': 'application/x-foo'}Passed

SHA-256 / d1bb1f96b545a432a3b6ba573a6bbc2b2aef15ffb0335fad8ebfa33bd67dd4d4

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(part, supported):
    def effective(p):
        if p['type'] == 'multipart/related':
            start = p.get('params', {}).get('start')
            for c in p['parts']:
                if start is not None and c.get('cid') == start.strip('<>'):
                    return c['type']
            return p['parts'][0]['type'] if p['parts'] else None
        return p['type']
    ok_charsets = ('us-ascii', 'utf-8', 'iso-8859-1')
    best = None
    for i, p in enumerate(part['parts']):
        t = effective(p)
        cs = p.get('params', {}).get('charset', 'us-ascii').lower()
        if t in supported and (not t.startswith('text/') or cs in ok_charsets):
            best = i
    if best is None:
        return {'index': 0, 'type': effective(part['parts'][0]), 'fallback': True}
    return {'index': best, 'type': effective(part['parts'][best]), 'fallback': False}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
_CASES = {1: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown1'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root1@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root1@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'ISO-8859-1'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 2: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown2'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root2@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root2@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'UTF-8'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 3: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown3'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root3@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root3@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'ISO-8859-1'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 4: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown4'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root4@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root4@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'UTF-8'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})], 5: [('richest supported last', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-amp-html'}]}, ['text/plain', 'text/html', 'text/x-amp-html']), {'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}), ('unsupported last part', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}, {'type': 'text/x-unknown5'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('related root via start', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'multipart/related', 'params': {'start': '<root5@x>'}, 'parts': [{'type': 'image/png', 'cid': 'img@x'}, {'type': 'text/html', 'cid': 'root5@x'}]}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('upper-case charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain', 'params': {'charset': 'UTF-8'}}, {'type': 'text/html', 'params': {'charset': 'ISO-8859-1'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('missing charset', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html'}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 1, 'type': 'text/html'}), ('unknown charset html', ({'type': 'multipart/alternative', 'parts': [{'type': 'text/plain'}, {'type': 'text/html', 'params': {'charset': 'x-klingon'}}]}, ['text/plain', 'text/html']), {'fallback': False, 'index': 0, 'type': 'text/plain'}), ('nothing supported', ({'type': 'multipart/alternative', 'parts': [{'type': 'application/x-foo'}, {'type': 'text/x-bar'}]}, ['text/plain']), {'fallback': True, 'index': 0, 'type': 'application/x-foo'})]}
for _label, _args, _expected in _CASES[N]:
    check(_label, solve(*_args), _expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
richest supported last{'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}{'fallback': False, 'index': 2, 'type': 'text/x-amp-html'}Passed
unsupported last part{'fallback': False, 'index': 1, 'type': 'text/html'}{'fallback': False, 'index': 1, 'type': 'text/html'}Passed
related root via start{'fallback': False, 'index': 1, 'type': 'text/html'}{'fallback': False, 'index': 1, 'type': 'text/html'}Passed
upper-case charset{'fallback': False, 'index': 1, 'type': 'text/html'}{'fallback': False, 'index': 1, 'type': 'text/html'}Passed
missing charset{'fallback': False, 'index': 1, 'type': 'text/html'}{'fallback': False, 'index': 1, 'type': 'text/html'}Passed
unknown charset html{'fallback': False, 'index': 0, 'type': 'text/plain'}{'fallback': False, 'index': 0, 'type': 'text/plain'}Passed
nothing supported{'fallback': True, 'index': 0, 'type': 'application/x-foo'}{'fallback': True, 'index': 0, 'type': 'application/x-foo'}Passed

SHA-256 / 2aedc2c63759913515e0d457a408af5dfedb8aa56be4c947e76fe1d6860e4b29

Verification & scope

Stipulated offline model over pre-parsed MIME dictionaries; not a conforming MIME parser, generator or mail client. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:49:15.441240+00:00.

Case digest / 1cca22467ab44cb8dd0cf1d9cc295c624fb1ae6df9cca7d7448bc59ba0068f16